1. Field of the Invention
The present invention relates to an apparatus and methods of improving shelf life of resins, and more particularly to a method for controlled purging of resin materials which prevents humid air from re-entering the purged material.
2. Description of Prior Art
Resinous materials are commonly used for a wide range of commercial activities in the manufacturing, machinery and electrical industries; but more particularly, in the electronics field. For example, resins are used for potting, embedding, encapsulating and coating applications. The resins typically employed in these applications have a potential shelf life of from six to twelve months. Under the conditions of normal day-to-day use, however, the shelf life is considerably shorter. Each time a can or drum is opened for use, the resin is freshly exposed to oxygen and humidity in the surrounding air. During successive openings of the can or drum, additional oxygen and water vapor are introduced to the remaining resin. The resulting chemical reactions which occur within the unused resin markedly affect the physical and chemical properties of the resin. Thus, initially, there is the problem of non-uniformity in successive uses of the same can of resin. Eventually, the deterioration of the resin properties progresses to the point where the remaining product is unsuitable and must be discarded.
Although the concept of "purging" containers using a stream of dry, inert gas is, broadly speaking, not a new one in the chemical arts, the purging of resin containers to help realize maximum potential shelf life of unused resin must meet certain special requirements. First, the amount of purging employed must be optimized. Because the purging operation, involving generally the use of a cylinder of compressed nitrogen or similar inert gas and a certain amount of human labor, is not costless, at least a rough cost-benefit analysis is required to determine the optimum level of oxygen and moisture which should be left in the resealed resin container. Once this optimum level of purging is ascertained, the apparatus employed must be capable of easily and reliably determining when that optimum level has been attained. The length of time required for reaching this optimal level will vary according to the size and void volume of the container, the length of time the resin has been exposed to the atmosphere, and the flow rate of the dry, inert gas.
In this connection, a second special problem which arises in purging a resin container to an optimal level of oxygen and moisture reduction is the danger of additional surrounding air leaking into the container as the purging operation is completed and the container sealed. Not only would such leakage introduce additional oxygen and moisture, thereby departing from the "optimal" level, but this situation would also lead to non-uniformity of the resin during successive uses.